Atlas of Pathos Chapter 6

Cardiomyopathy

C ardiomyopathy is classified as dilated, hypertrophic, or restrictive. Dilated cardiomyopathy (DCM) results from damage to car- diac muscle fibers; loss of muscle tone grossly dilates all four chambers of the heart, giving the heart a globular shape. Hypertrophic cardiomyopathy (HCM) is characterized by dis- proportionate, asymmetrical thickening of the interventricular septum and left ventricular hypertrophy. Restrictive cardiomyopathy (RCM) is characterized by restricted ventricular filling due to decreased ventricular com- pliance and endocardial fibrosis and thickening. If severe, it’s irreversible. Causes Most patients with cardiomyopathy have idiopathic disease, but some are secondary to these possible causes: • viral infection • long-standing hypertension • ischemic heart disease or valvular disease • chemotherapy • cardiotoxic effects of drugs or alcohol • metabolic disease, such as diabetes or thyroid disease. Pathophysiology In DCM, extensive damage to cardiac muscle fibers reduces contractility in the left ventricle. As systolic function declines, stroke volume, ejection fraction, and cardiac output fall.

Complications • Heart failure • Arrhythmias • Emboli • Sudden death

Signs and Symptoms • Shortness of breath • Peripheral edema • Fatigue • Weight gain • Cough and congestion • Nausea • Bloating • Palpitations • Syncope • Chest pain • Tachycardia DiagnosticTest Results

• Chest X-rays show cardiomegaly and increase in heart size. • Echocardiography reveals left ventricular dilation and dys- function or left ventricular hypertrophy and a thick, asym- metrical intraventricular septum. It can also quantify the outlet left ventricular outflow gradient in HCM. • Cardiac catheterization shows left ventricular dilation and dysfunction, elevated left ventricular and, commonly, right ventricular filling pressures, and diminished cardiac output. • Thallium or cardiolite scan usually reveals myocardial perfu- sion defects. • Cardiac catheterization reveals elevated left ventricular end- diastolic pressure and, possibly, mitral insufficiency. • ECG usually shows left ventricular hypertrophy; ST-segment and T-wave abnormalities; Q waves in leads II, III, and aV F , and in V 4 to V 6 ; left anterior hemiblock; left axis deviation; and ventricular and atrial arrhythmias. Treatment • Treatment of underlying cause • Control of arrhythmias • Angiotensin-converting enzyme inhibitors, diuretics, digoxin (not used in HCM), hydralazine, isosorbide dini- trate, beta-adrenergic blockers, antiarrhythmics, and anticoagulants • Revascularization • Valve repair or replacement • Heart transplantation • Lifestyle modifications, such as quitting smoking; avoiding alcohol; eating a low-fat, low-salt diet; and restricting fluids • Ventricular myotomy or myectomy • Mitral valve repair or replacement • Defibrillator placement with or without biventricular pacing

Complications • Heart failure • Emboli • Syncope • Sudden death

In HCM, hypertrophy of the left ventricle and interven- tricular septum obstruct left ventricular outflow. The heart compensates for the decreased cardiac output (caused by obstructed outflow) by increasing the rate and force of con- tractions. The hypertrophied ventricle becomes stiff and unable to relax and fill during diastole. As left ventricular volume diminishes and filling pressure rises, pulmonary venous pressure also rises, leading to venous congestion and dyspnea.

Complications • Pulmonary hypertension

• Heart failure • Sudden death

In RCM, left ventricular hypertrophy and endocardial fibro- sis limit myocardial contraction and emptying during systole as well as ventricular relaxation and filling during diastole. As a result, cardiac output falls.

54  Part II • Disorders